cubicweb-mercurial-server #3252323 make sure ssh always uses the right key [validation pending]

prioritynormal
typebug
done in0.4.0
load0.500
load left0.000
closed by#35c5b6696924 [utils] tell ssh to obey IdentityFile from ssh_config (closes #3252323)
patch[utils] tell ssh to obey IdentityFile from ssh_config [applied]